Both during and following fabrication, integrated circuit manufacturers test to determine that their integrated circuits satisfy design specifications. These tests typically involve the use of test probe cards that use test heads comprising a plurality of pins. The test pins are usually metal needles or blades that make electrical contact with test nodes or pads on the integrated circuits.
Conventional test heads that use metal needles or blades suffer from several limitations. First of all, conventional test head designers connect the metal needles to bonding wires on a printed circuit board by hand using manual alignment methods. This is a tedious process that makes conventional test probes extremely expensive. Also, conventional integrated circuit testing devices, because of their needle and wire bonding configurations have both size and complexity limitations. However, with today's integrated circuits increasing in size and complexity, the number of test nodes on an integrated circuit and, accordingly, the number of needles on test heads for testing these circuits must increase. The input and output speed of test signals through the test head, additionally, must increase.
With these requirements, conventional integrated circuit test probes have input/output limitations that are incompatible with or insufficient to meet the testing needs of new and more complex integrated circuits. Moreover, as the number of pins increase, their likelihood of being misaligned, bent, or shorted together increases, thereby shortening their functional lives.
The needles of conventional test heads also have significant physical length relative to their signal wave lengths. As a result, they suffer from capacitances and inductances that reduce input/output signal transmission speeds between the integrated circuits and the testing circuitry.
Today's testing systems are also becoming increasingly automated and complex. Automated prober systems for integrated circuits help to reduce operator intervention during the test process. New prober systems offer greater accuracy and longer life and improve productivity through features such as automatic wafer alignment and profiling. Some of the latest probers incorporate on-line systems which automatically evaluate and correct, if necessary, testing circuitry features such as contact impedance. The systems can accommodate even more complex test probe cards than are presently available.
In an attempt to solve the limitations inherent in conventional integrated circuit test heads, a thin film test probe is described in C. Barsotti et al., "New Probe Cards Replace Needle Types," Semiconductor International, p. 98 (Aug. 1, 1988). That device (the "Barsotti device") provides a high density and high performance test head that uses a metallic contact pad configuration to provide a more reliable test signal communication path and decrease parasitic capacitance and inductance in test signal transmission. The Barsotti device includes a test probe that comprises an elastomer base with a ground plane and polyimide layer covering the ground plane. The polyimide layer insulates the ground plane from the elastomer base. Strip lines cover the polyimide layer and connect to the metallic contact pads. The metallic contact pads engage test nodes on the integrated circuit to be tested.
Though the Barsotti device represents an improvement in integrated circuit testing technology, it still suffers from severe limitations. The Barsotti device increases the performance of integrated circuit testing, but at a significantly increased cost to the tester. Other limitations associated with the test probe include, first of all, that the elastomer base test probe requires the use of non-conventional fabrication techniques. Additionally, the polyimide and ground plane layers of the Barsotti device are bent to provide a protruded surface from which the metallic contact pads can extend. The protruded surface of the Barsotti device can cause signal degradation as it passes through the bent stress areas of the polyimide layer and ground plane.
Yet another limitation of known test probes is that in the event of a defect or misalignment of the needle pins of conventional test probes or a defect in the contact pads of the Barsotti device, the entire test probe must be discarded. If a device existed to permit rapid replacement of only the defective or damaged portion of the test head, manufacturers could realize significant savings during integrated circuit testing.
Consequently, there is a need for a low cost integrated circuit test head that provides high performance integrated circuit testing and which overcomes many of the limitations associated with test heads that use metal needles or blades.
Furthermore, a need exists for a disposable high performance test head for integrated circuits that permits removal of only the portion of the test head that may be damaged or defective.